1. Field of the Invention
The present invention generally relates to lubricant supply systems for four-cycle internal combustion engines used in powering watercraft. More particularly, the present invention relates to cooling systems for the lubricant supply systems of such engines.
2. Related Art
Watercraft are commonly powered by internal combustion engines contained within outboard motors. These motors have a water propulsion device, such as a propeller, which is driven by an output shaft of the internal combustion engine. The engine is also typically mounted within an enclosed cowling of the motor.
As is well known to those of ordinary skill in the art, internal combustion engines, particularly four-cycle internal combustion engines, require lubricant that is supplied to a crank chamber and other moving components of the engine by a lubricant pump. In general, the lubricant circulates between a crank chamber of the engines and a lubricant pan associated with the engines. These lubrication systems are arranged to provide lubricant from a supply to one or more galleries which, in turn, supply lubricant to bearings and other moving components of the internal combustion engines.
The lubricant being circulated within the engine is prone to great fluctuations in temperature. For instance, the crank chamber is exposed to substantial combustion heat (i.e., heat that results from the ignition of an air fuel charge within the combustion chamber). Thus, the temperature inside the crank chamber increases. Accordingly, the temperature of the lubricant passing through the crank chamber also rises. In some instances, the temperature of the lubricant may rise above 150xc2x0 C. This elevated temperature creates problems, such as rapid degradation of lubricant quality and poor lubricant performance.
Preferably, the lubricant is maintained within an optimal operating temperature range. In some applications, the optimal operating temperature range is between about 60xc2x0 C. to about 80xc2x0 C. When the temperature of the lubricant is less than about 60xc2x0 C., it becomes difficult to pump and flows less freely through the lubricating system and through the engine. On the other hand, when the temperature of the lubricant exceeds 80xc2x0 C., the lubricant begins to thin and becomes less effective in forming a protective film over moving components of the engine.
Accordingly, some lubricant supply systems have been provided with lubricant cooling systems to prevent the lubricant from overheating. In some such lubricant cooling systems, heat exchangers are provided. The heat exchangers may use cooling water that is supplied from the body of water in which the watercraft is operating. Thus, the lubricant flowing through the heat exchangers may be cooled by the lower temperature cooling water flowing through the heat exchanger and back into the body of water in which the watercraft is operating. According to this arrangement, a fixed flow rate of coolant is provided to the heat exchanger.
The fixed flow rate has a tendency of overcooling the lubricant when the engine is operating at a low speed or when the engine temperature is low. Accordingly, the coolant flow rate through the heat exchanger may be fixed at a rate which does not overcool the lubricant (i.e., a low flow rate). However, this arrangement provides insufficient cooling to the lubricant when the engine temperature increases (i.e., during high speed operation). Moreover, especially for outboard motors, the coolant being drawn from a lake or ocean to be used as to the coolant, may have an exceedingly low temperature, thus even with a low flow rate, the lubricant may be cooled more than desired.
In an attempt to correct this overcooling, another type of lubricant cooling system has been developed. In this cooling system, a flow adjusting valve is provided within the coolant passage in which the coolant flow rate flowing to the heat exchanger is adjustable by opening and closing the valve, depending on the actual temperature of the lubricant. While providing a viable solution, this system is not without its disadvantages. For instance, fluctuations in the coolant flow rate may cause a negative load at the water pump. The negative load may deteriorate the operability of the water pump over time. Moreover, in watercraft being operated in saltwater environments, salt deposits may form on the adjusting valve, which salt deposits may eventually inhibit the long range usefulness of the lubricant cooling system.
Accordingly, an improved lubricant cooling system is desired. The system preferably reduces a fluctuation in lubricant temperature by increasing a heat transmission level between coolant and lubricant when the lubricant temperature is above a first predetermined temperature and reducing a heat transmission level between coolant and lubricant when the lubricant temperature is below a second predetermined temperature.
One aspect of the present invention involves a recirculating lubrication system comprising a lubricant supply and a lubricant supply passage extending from the supply to a crank chamber of an engine. A heat exchanger forms at least a portion of the lubricant supply passage with a bypass valve being interposed between the lubricant supply and the heat exchanger along the lubricant supply passage. A bypass conduit is connected to the bypass valve at a first end and the supply passage downstream of the heat exchanger at a second end. A temperature sensor is positioned along the supply passage with the temperature sensor being capable of detecting a temperature of the lubricant. The bypass valve is configured to alter a flow rate through at least one of the bypass conduit and the heat exchanger to regulate the temperature of the lubricant.
Another aspect of the present invention involves a four cycle outboard motor that comprises a lubrication system having a heat exchanger and a cooling system that delivers coolant to the heat exchanger. The lubrication system comprises a lubricant supply, a lubricant supply passage that extends from the lubricant supply to a crank chamber of the engine. The heat exchanger forms a portion of the lubricant supply passage. A lubricant temperature sensor is positioned along the lubricant supply passage and is capable of detects a temperature of lubricant passing through the lubricant supply passage. The cooling system comprises a coolant supply, a coolant supply passage that extends between the coolant supply and the heat exchanger and a coolant supply bypass valve that is positioned along the coolant supply passage between the coolant supply and the heat exchanger. A coolant supply bypass conduit communicates with the coolant supply passage through the coolant supply bypass valve. The coolant supply bypass valve is capable of selectively diverting at least a portion of the coolant delivered through the coolant supply passage away from the heat exchanger through the coolant bypass conduit.